Cable television (CATV) operators provide cable television and other services such as Internet connectivity and digital telephone service. The CATV network may include fiber optic and coaxial cables that provide bidirectional transport of radio frequency (RF) signals. Customers may connect to the CATV network utilizing cables to connect to a main transmission line via taps in the main transmission line.
FIG. 1 illustrates an example block diagram of a CATV network 100 utilizing a tap 110 on a main transmission line 120 to provide connectivity to a customer via cables 130. The tap 110 receives RF signals on the main transmission line 120 from a central office (upstream) and transmits the RF signals downstream over the main transmission line 120. The tap 110 may also receive RF signals from downstream and transmit the RF signals upstream. The tap 110 may include RF circuitry 140 to process the RF signals destined for the customer so the RF signals can be provided to the customer via the cable 130. Likewise, RF signals received from the customer via the cable 130 may be processed so they can be transmitted via the main transmission line 120.
In addition to providing the processing of the RF signals necessary for communication with the customer, the RF circuitry 140 may provide a conduit (transmission line) for continued communications over the main transmission line 120. The tap 110 may include a bypass line 150 that provides an alternative conduit (transmission line) for maintaining communications over the main transmission line 120 in the event that the RF circuitry 140 is removed from the path for any reason (e.g., failure, maintenance, repair, upgrade).
The taps may include a housing and a tap plate. The housing may include connectors to secure ends of the main transmission line 120 and to provide RF shielding. The tap plate may include the RF circuitry 140 to perform necessary processing of the RF signals for communications with the customer. The tap plate may also include on or more connectors for providing connectivity to the customer via cables connected thereto. The tap plate may also provide a transmission line to allow the RF signals and power to pass therethrough. The bypass line 150 may be located within the housing and be utilized when the tap plate is removed from the circuit (e.g., removed for maintenance).
FIG. 2 illustrates an example tap 200 with the tap plate (RF circuitry) removed. The tap includes a housing 210 that has an input connector 220 to connect to and receive the main transmission line 205 from upstream and a connector 230 to connect to and provide the main transmission line 205 to downstream. The tap 200 includes interfaces 225, 235 (conductors) in communication with the main transmission line 205 via the connectors 220, 230. When the tap plate (RF circuitry) is installed the interfaces 225, 235 are also in communication with the tap plate. In the downstream direction, the interface 225 is used to provide the RF signals and power from the main transmission line 205 to the tap plate and the interface 235 is used to provide the RF signals and power from the tap plate to the main transmission line 205. The tap plate provides a conduit (transmission line) for communications between ends of the main transmission line 205 connected to the tap 200.
The tap 200 also includes a bypass line 240 to provide an alternative conduit (transmission line) to maintain communications between ends of the main transmission line 205 when the tap plate is removed. The bypass line 240 may be capable of being connected or disconnected from the connectors 220, 230 based on whether the tap plate is installed or not. For example, the bypass line 240 may be connected to conductive movable shafts that may be connected to the connectors 220, 230. When the tap plate is installed, the conductive movable shafts may be pushed down so as not to be connected to the connectors 220, 230. Since the conductive movable shafts are not connected to the connectors 220, 230 the bypass line 240 is not in communication with the connectors 220, 230. When the tap plate is removed (off), the conductive movable shafts may shift up and contact the connectors 220, 230. Since the conductive movable shafts are connected to the connectors 220, 230 the bypass line 240 is in communication with the connectors 220, 230 and acts as the conduit to maintain communications between ends of the main transmission line 205.
Present CATV taps 200 may provide a bandwidth of 1 GHz. With additional services being provided over the CATV network and the increased desire for faster download and/or upload speeds, there is a desire for additional bandwidth. The bandwidth may currently be limited to 1 GHz due to electrical limitations of the current tap plate as well as mechanical design features of the tap 200.
When the tap plate is installed, the bypass line 240 is disengaged but still presents a transfer impedance that is in parallel to the tap plate (RF input to output electronics). The bypass line 240 responds to the RF parameters within the tap 200 to produce resonances that occur above 1 GHz (at approximately 1.2 GHz). These resonances significantly influence the tap's input to output insertion loss and limit extending the tap bandwidth above 1 GHz (may be able to extend the bandwidth to 1.2 GHz with a new tap plate). The bandwidth may not be extended above 1 GHz (or possibly 1.2 GHz) unless the entire tap is replaced to modify the response of the bypass lines 240 to the RF. Replacing the entire tap requires physically removing the existing tap and replacing it with a new tap. This would require a significant time and cost investment by the CATV operator.
FIG. 3 illustrates an example graph of the input to output insertion loss of a conventional (present field-installed) tap. As illustrated, at approximately 1.2 GHz the loss increases by approximately 3 db and this increase in loss prevents extending the bandwidth above this point.
Being able to extend the bandwidth of the taps without having to physically replace the current taps with new taps would dramatically improve the cost and down time of future RF network upgrades beyond 1 GHz.